Art of phosphoric acid manufacture



l. HECHENBLEIKNER Apr-i124, 192s. 1,667,549

ART OF PHOSPHORIC ACID MANUFACTUBE Filed April l. 1924 Patented Apr'. 24, 192s.

UNITED f s'rakrEs or cnABLoTTn NonTn cAnoLINA, AssIoNon To` :NGENUIN HEcnENBLEIxNEn,

cnmrrcAL CONSTRUCTION NoETH cAaoLINA.

COMPANY, F NEW YORK,

Nf Y., A CORPORATION 0F ABT or 'rnosrnonrc Acrn IANUrAcTunE.

Application -led April I,

'This invention relates to the art of phosphoric acid manufacture, and relates more particularly to `an improved method ofobtaining phosphoric acid 'by the wet grinding of a calcium phosphate containing rock in the presence of hosphoric acid, added at the time of g or `produced by the addition of another acid, such as sulphurlc. In the manufacture of phosphoric acid hy reacting phosphate rock with sulphuric acld in'accordance with prior methods, the calcium phosphate containing rock is rst ground in a mill in a dry state to produce an impalpable powder; and a chargeof the ground phosphate rock is mixed with sulphuric acid in a mixer or agitator, the phosphate rock particles reacting with the sulphuric acid to produce phosphoric acid and calcium sulphate. The products of reaction are then introduced into a separator, where the phosphoric acid is separated from the calcium sulphate residue.

A prime desideratum of our present invention relates to improvements in this method of phosphoric acid manufacture in which the reactions are carried on with increased speed and eiliciency, and in which v the process as a wholeis practiced with greater speed, economy and convenience. 3o Thegrinding ofthe phosphate rock in a dry state as heretofore practiced presents operating difficulties, among which-*are the slowness of'the grinding step, and the necessity of handling in separate steps the rock and the ground material. The reacting of the powdered phosphaterock with sulphuric acid also presents operative Y diiiiculties among which is the necessity for effecting a very intimate mechanical intermixture be- 40 tween the powdered rock and the liquid re agent to produce the desired reaction. By Y the present invention, it is contemplated to obviate these disadvantages, the grinding and mixing operations of the process being modified to effect-a more intimate reaction of` the phosphate rock and amore expeditious carrying out ofthe grinding and mixin steps of the method. v

e .have discovered that the phosphate rock instead of being separately ground in a dried state and then mixed for reaction with sulphuric acid may be subjected to Y the treatment of phosphoric acid, the grind- 1934.v Serial No. 703,460.

ing of therockin the presence of the acid eliminating the prior necessity of separately handling the powdered rock and the objections incident to 4dry grinding, and edecting a more intimate reaction between the acid and the rock than has been found possible in the mixing step of the method as heretofore practiced..l One of theprincipal objects of the present invention centers about the production ofsoluble phosphates in a continuous process, by the wet grinding of the rock in the. usual mill, in. the presence of dilute phosphoric acid supplied continuously o'r by additions-'in quantity sufficient to provide an overflow of the dilute acid and the fluent product of the grinding. The overflow is reacted with sulphuric acid, and

a portlon of the dilute phosphoric acid d1- verted to the grinding operation.

We have discovered by operating in this -manner that the process maybe considerably hastened, and the reaction speeded, lwith the use of simplified apparatus, since by wet grinding with the sulphuric acid phosphoric acid is produced, thus dispensmg with ,the steps of handling the ground rock-andrmixing with sulphuric acid in a mixer to obtain the phosphoric acid. -A further-objectof the invention therefor comprehends the use of sulphuric acid in theinitial grinding `operation.

To the accomplishment of the foregoing andsuch other objects as may lhereinafter appear, our invention consists in the process, the steps of the process and ,their relation one/to the other, as hereinafter articularly described and sought to be defined inthe claims; reference being had to the accompanying `drawing which shows a preferred orm of our invention, and in which:

v'The figure isa view showingl in diagrammatic form a phosphoric acid plant emp oyed in the practice of the method.

In carrying 4out the operation, coarse phosphate rock is ground in the presence of phosphoric acid, and to facilitate and s eed up the process sulphuric acid may be a ded to the initial batch to produce the phosphoricr acid.

In the subsequent operations of the proc-k ess, the coarse phosphate rock isground in the. presence of a` dilute phosphoric acid, which preferably is obtained fromv one of the separators, the grinding of the rock. in phosphoric acid producing aprimary reack tion in which Vmono calclum phosphate is obtained7 in accordance with the following formula:

(b) Camo.) +H.SO.

The products of this secondary reaction are then fed into a separator where the hosphoric 'acid is separated from ,the resiue or slurry calcium sulphate. It will be i noted-'that by subdividing the treatment o' the rock into the primary and secondary reaction stages, we are enabled to ei'ect a moist grinding of the rock with its attend- 4 ant advantages, and a moreintimate reaction between the rock and the acid than can beobtained ina mechanical mixer. A further advantage of this process isjthe production of the mono calcium phosphate, which being water-soluble, is introduced into the` 4mixer in a liquid@ state, this liquid reacting with the sulphric acid withgreater facility and speed than is obtaned in prior methods by the reaction of the impalpable powder with thesulphuric acid. It will also be observed that since the mono calcium phosphate is water-solublefthe precipitation of' sulphuric acid products such as calcium sul- Ell/1ste in the mill is prevented. It has also, i

, v n found that the practice of thi's method permits the obtaining of a more concentrated product after separation, minimizing.

subsequent concentration steps, and that acleaner. washing isobtained in the separatinsteps of the method.-

ferring now toathe drawing, in which we showtheapparatus employed in the practice of the method, we provide the usual mill J10, into which is fed' coarse rock from a coarse-rock bin or compartment 11 through a duct 12, the feed through which is regulated by meansv of a regulator 13, Into this mill in the beginning of the process is' vfed sulphuric acid, and afterwards is fed dilute phosphoric acid taken from one of the separators, as will be shown 'more hereinafter, and ccnducted throughthe'pipe 14 having entry into the .mi1l,.the phosphoric acid belmg if desired diluted bymixing the same wlth water obtainedfrom awater tank 15 and .fed into the mill through a pipe 16 controlled by a valve 17.

The mono vcalcmm'phosphate obtained in 11,1304 and (MS04. p

pump 29V into the tank 18 into whichv sulphuric vacid is ins troduced from a sulphuric acid.4v tank 19 through a pipe 20, the ilow of whichvis controlled by a valve 21, the said mixer being provided with the usual agitati'ng or mixing device 22. The secondary reaction between the liquid mono calcium phosphate and the sulphuric acid here takes place, the products of reaction consisting of the calcium sulphate andthe phosphoric acid overlowingv and feeding into the separating tank 23. It will be understood that although one mixer is shown lin 'the drawings, that in practice a plurality of these mixers arranged incascade or series may be and lare emloyed.

gravity type, in which the phosphoric acid is separated from' the sludgeg or waste, the former having exit at` 24 to a pipe 25 connected to a storage reservoir, and the latter The separating tank 23 may be of the having exit at 26 into a waste pipe 27 which may be controlled by a valve 28. Although oneseparator has been shown in the drawings, it will bev understood that` a plurality of separators also arranged in cascade or series may be and 'are employed in practice.

-The dilute phosphoric acid which is employed for reaction with the phos hate rock in the mill is take'n from one o the separators, this l being shown diagrammaticallyn in the drawing, said phosphoric acid being pumped fromthe pipe 25 by means df the pipe 14' connected to the grinding mill.

The practice of the method, use of the apparatus, and the advantages theref, will in the main be fully apparent from the above detailed description thereof taken inconnection with the operation. It will be further apparent that many changes may be made in the apparatus disclosed and in thesteps of the method without departing from the spirit of the invention defined in the following claims. -For example, the separation between the liquid an'd the slurry or sludge in the last step -of; the method may be effected in any manner well known' in the art, as for example by the employment of filters in'lieu of mechanical separators. Itwilllthus be apparent that numerous rearrangements and .changes may be made without modifying the principle of the present invention.

I claim: J

A1. The herein described continuous method i of producing phosphoric acid from phosphate I rock, which consists A in grinding the rock in phosphoricacid with additions of dilute phosphoric acid suiiicient to provide a-substantially continuous overiow of acid 1,607,549- p A B of producing phosphoric acid 'f1-om. phos; liquid from the sludge, and diverting a. por phate rock, which consists in the tion of the liquid to the rock being ground l. rock in dilute phosphoric acid with additions to provide a selected strength of acid for the of dilute phosphoric acid sufficient to prognnding.

v5 vide a. substantially continuous overflow of Signed at New York city in the county of acid and the iiuent product o'f the grinding, New York and State of New York this 29thv treating-.the overflow with sulphuric acid to day of March A. D. 1924. precipitate calcium sulphate, vseparating the INGENUIN HECHENBLEIKNER. 

